Sonographic Appearance ofAngioedema in Local Allergic Reactionsto Insect Bites and Stings

oft tissue swelling related to insect bites and stings is acommon presentation in the emergency department (ED).Differentiating between cellulitis and angioedema caused

by a local allergic reaction on visual inspection may be difficult,especially when evidence of an insect bite or sting is not apparent.1This diagnostic uncertainty may lead to the overuse of antibioticswhen cellulitis is not present. Although previous studies have usedsonography to describe the characteristics of cellulitis and skinabscesses, none have described the sonographic findings ofangioedema caused by local allergic reactions.2–9

Here, we describe 4 cases of patients who presented with softtissue swelling from insect bites or stings and their point-of-caresonographic appearances of angioedema caused by local allergicreactions.

Case Descriptions

Case 1A 5-year-old girl presented with a swollen right hand for 1 day.A small pruritic “pimple” was noted the day before and was sus-pected to be an insect bite. Her hand became progressively swollenthroughout the day of presentation. She was afebrile, and no med-ication was given at home. Physical examination showed a non-tender, erythematous, swollen right hand with fluctuance and acentral punctum (Figure 1A). No induration or crepitus was noted.

Ee Tein Tay, MD, James W. Tsung, MD, MPH

Received November 18, 2013, from the Departmentsof Emergency Medicine and Pediatrics, IcahnSchool of Medicine at Mount Sinai, New York,New York USA. Revision requested December 5,2013. Revised manuscript accepted for publicationJanuary 10, 2014.

Address correspondence to Ee Tein Tay, MD,Department of Emergency Medicine, Icahn Schoolof Medicine at Mount Sinai, 1 Gustave Levy Pl,1149, New York, NY 10029 USA.

E-mail: eetaymd@gmail.com

AbbreviationsED, emergency department

S

©2014 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2014; 33:1705–1710 | 0278-4297 | www.aium.org

CASE SERIES

Soft tissue infections and angioedema from insect bites and stings may be difficult to dif-ferentiate by inspection. We present sonographic findings of 4 cases of soft tissueswelling from insect bites and stings suggestive of angioedema. Sonographic featuresof soft tissue angioedema consist of thickened subcutaneous tissue layers with multiplelinear, horizontal, striated, and hypoechoic lines following the tissue planes betweensoft tissue layers. In addition to the history and physical examination, sonographic find-ings may assist in differentiating between local allergic reactions and cellulitis in patientswith insect bites and stings. Further study is warranted for clinical application.

Key Words—allergic reaction; angioedema; insect bites; insect stings; point-of-careultrasound; sonography

doi:10.7863/ultra.33.9.1705

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Case 2An 8-year-old boy presented with a swollen right foot for1 day. He had tried to step on wasps with his bare footthe day before and thought he may have been stung in theprocess. He had mild pruritus and a subjective fever. Nomedications were given at home. Physical examinationrevealed an afebrile patient with a swollen, erythematousdorsal right foot with mild induration (Figure 2A). No fluc-tuance, crepitus, calor, or tenderness was appreciated on pal-pation. Several puncta were noted on the dorsal foot butnone on the plantar surface.

Case 3A 4-year-old boy presented with a swollen right hand froman insect bite earlier in the day. He had pruritus withoutpain and was afebrile. The hand became progressivelyswollen throughout the day. No medications were givenat home. Physical examination showed a swollen, fluctuant,nontender right hand without calor, induration, or crepitus(Figure 3A). A punctum was noted on the dorsal hand.

Tay and Tsung—Angioedema in Local Allergic Reactions to Insect Bites and Stings

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Figure 2. Case 2. A, Right foot swelling and erythema compared to the

normal left foot. B, Transverse sonographic view of right foot swelling.

C, Transverse sonographic view of the normal left foot.

A

BFigure 1. Case 1. A, Right hand swelling with a central punctum com-

pared to the normal left hand. B, Transverse sonographic view of right

hand swelling.

A

B

C

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Case 4A 3-year-old boy presented with a swollen left upper eye-lid and left side of the forehead for 1 day after sustainingan insect bite to the forehead. Topical hydrocortisone wasapplied for pruritus without improvement. Physical exam-ination revealed an afebrile child with multiple puncta onthe left forehead and a swollen left upper eyelid (Figure 4A).There was mild erythema around the puncta and over theleft upper eyelid. No induration, fluctuance, crepitus, ortenderness on palpation was noted on examination.

Scan TechniqueSonography was performed with an M-Turbo ultrasoundmachine and a high-resolution 13–6-MHz linear arraytransducer (SonoSite, Inc, Bothell, WA). Sonography ofthe extremities was performed by a water bath technique.Conventional linear array scans without spatial compound-

ing or Doppler imaging were performed. Transverse andlongitudinal views were obtained over the area of maxi-mum swelling.

Sonography in all 4 cases showed thickened subcuta-neous tissue layers with multiple linear, striated, horizon-tal, and hypoechoic lines following the tissue planesbetween soft tissue layers (Figures 1B, 2B, 3B, and 4B).The hypoechoic lines were located within the subcuta-neous tissue, sparing muscle tissue. The thickness and loca-tion of these lines varied within the soft tissue plane: eithersuperficial, deep within the tissue, or both. The extremitiesappeared to have more thickened soft tissue and linear linesthan areas with limited room for tissue expansion, such as

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Tay and Tsung—Angioedema in Local Allergic Reactions to Insect Bites and Stings

Figure 3. A, Right hand swelling compared to the normal left hand.

B, Transverse sonographic view of right hand swelling.

A

B

Figure 4. Case 4. A, Left upper eyelid swelling with lateral forehead ery-

thema compared to the normal right eyelid. B, Transverse sonographic

view of left upper eyelid swelling. C, Transverse sonographic view of the

normal right eyelid.

A

B

C

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the eyelid. There were no distinct margins or increases ordecreases in the echogenicity of the affected tissue. Whencompared, sonography of the contralateral sides did notshow thickened skin or linear, horizontal, and striated lines(Figures 2C and 4C). These findings were seen in bothtransverse and longitudinal views.

Discussion

The use of point-of-care sonography for soft tissue eval-uations in the ED has predominantly been used for thedetection of infections in cutaneous cellulitis and abscesses,peritonsillar abscesses, and necrotizing fasciitis.2–9 Previousstudies have used sonography to measure subcutaneousskin thicknesses from limb swelling in immunization reac-tions and evaluation of soft tissue thicknesses in responseto patch test reactions on A-mode sonography,10,11 but nonehave described the appearances of soft tissue angioedemacaused by local allergic reactions on B-mode scans.

Based on our cases, soft tissue angioedema in localallergic reactions from insect bites and stings appears to bethickened on sonography with multiple, linear, horizontal,and striated hypoechoic bands within the tissue (Figure 5A).Sonographic features of cellulitis on sonography includeskin thickening, subcutaneous edema, and the appearanceof haziness and fluid surrounding fat globules, termed“cobblestoning”2–9 (Figure 5B). As cellulitis may be diffi-cult to discern from a local allergic reaction on physicalexamination because of similar findings on inspection,1 theclinical history in conjunction with sonographic featuresmay assist in diagnosis and management. Patients with cel-lulitis would be expected to have skin swelling, tendernesson palpation overlying the affected area, calor, and expan-sion of erythema from the initial site, and fever may oftendevelop. In patients with angioedema, physical findingsmay include skin swelling with the presence of puncta, skinerythema, excoriation from pruritus, and often tendernessin areas with less room for tissue expansion. Findings fromlocal allergic reactions are more immediate, usually peak-ing at 24 to 48 hours,12 whereas cellulitis tends to developlater in the course.

Cellulitis from insect bites and stings may also occur.1,13

As we compiled this case series, we encountered a patientwith 3 days of left calf redness and tenderness surroundinga punctum from a spider bite (Figure 6A). Sonography ofhis left calf showed skin thickening, haziness, and a swirling,cobblestone-like soft tissue pattern suggesting early cellulitiswhen compared to his normal left calf (Figure 6, B and C).The subcutaneous horizontal hypoechoic bands suggest-ing angioedema were absent on sonography in this patient.

This case supports the idea that it may be possible todevelop cellulitis from insect bites and stings,1,13 and with ahistory and physical examination, the use of sonography mayassist in distinguishing between cellulitis and angioedema.

In all 4 cases, antibiotics were not prescribed, andpatients were discharged with antihistamines for local allergicreactions. Patients were instructed to return to the ED ifthey developed increased redness, fever, calor, or pain atthe bite or sting sites. Although none of the patientsreturned to our ED for further evaluation of skin findings,this fact does not exclude the possibility that the patientsmay have been followed at other institutions for furthermedical care.

Previous cases have described the development ofcellulitis from insect bites and stings and their associationwith methicillin-resistant Staphylococcus aureus andmethicillin-sensitive S aureus infections.1,14,15 Cellulitis hasalso been mistaken as spider bites and has been subse-quently cultured as methicillin-resistant S aureus infec-tions.16 Antibiotic resistance has been increasing worldwidedue to factors such as overprescription of antibiotics anddevelopment of different resistant strains of bacteria.17,18

Tay and Tsung—Angioedema in Local Allergic Reactions to Insect Bites and Stings

J Ultrasound Med 2014; 33:1705–17101708

Figure 5. A, Horizontal linear bands of edema in angioedema on

sonography. B, Example of cobblestoning in cellulitis on sonography.

A

B

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With the emergence of antibiotic resistance, it is possiblethat sonography may assist in promoting antibiotic stew-ardship by evaluating whether infections are present andwhether antibiotics are warranted.

In summary, multiple horizontal bands of edema withinthe thickened soft tissue on sonography appear to suggestangioedema in patients with local allergic reactions to insectbites and stings. Although further studies are warranted for

clinical application of these findings, we hope that sonog-raphy may be used as an adjunctive tool in conjunctionwith the history and physical examination to assist in dif-ferentiating between cellulitis and allergic reactions andultimately promoting judicious prescription of antibioticsand antibiotic stewardship.

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15. Cohen PR. Community-acquired methicillin-resistant Staphylococcusaureus skin infections: implications for patients and practitioners. Am JClin Dermatol 2007; 8:259–270.

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Tay and Tsung—Angioedema in Local Allergic Reactions to Insect Bites and Stings

Figure 6. A, Left calf of a patient with a recent spider bite. B and C, Trans-

verse sonographic view of the affected left calf (B) suggesting cellulitis

compared to a transverse view of the normal right calf (C).

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B

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16. Segarra-Newnham M. Skin infections with methicillin-resistant Staphylococcus aureus presenting as insect or spider bites. Am J Health SystPharm 2006; 63:2046–2048.

17. Tenover FC, Hughes JM. The challenges of emerging infectious diseases:development and spread of multiply-resistant bacterial pathogens. JAMA1996; 275:300–304.

18. Huges JM, Tenover FC. Approaches to limiting emergency of antimi-crobial resistance in bacteria in human populations. Clin Infect Dis 1997;24(suppl 1):S131–S135.

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